1. Field of the Invention
The present invention relates to an apparatus, system and method for withdrawing a fluid from a test tube, and more particularly to a system for withdrawing and dispensing a biological fluid such as blood serum. The present invention is more specifically directed to a method and apparatus for continuously and automatically aliquotting a fluid, such as blood serum.
2. Description of the Prior Art
Processes for manipulating sample fluids, generally body fluids such as blood or urine, are conducted on a large scale in laboratories and hospitals. In the prior art process of collecting blood serum for example, blood is generally drawn into a vacuum test tube and centrifuged to separate the blood components from serum. This process is usually conducted by a technician, who draws blood into a vacuum test tube. The vacuum test tube generally contains a separating gel to separate the fluid contents into three layers: a top layer containing the serum, a middle layer containing the separating gel, and a bottom layer containing plasma. For purposes of the present invention, the term "plasma" is used to identify the whole blood components as opposed to serum. An example of a whole blood components are the red blood cells. The test tube must be centrifuged to separate plasma from serum.
After the test tube has been centrifuged, it is examined to determine whether the components have sufficiently separated to be accepted for further testing. If the sample fluid is acceptable, the serum is removed from the test tube in one of two ways: 1) the cap is removed from the tube and the serum is hand-poured into another receptacle; or 2) a needle is inserted through the cap in the top serum layer such that the end of the needle is at a position adjacent, but not touching, the middle separating gel layer. It is extremely important not to touch the needle to the middle layer to avoid plugging up the needle.
The disadvantage of the first method of removing serum, i.e., hand-pouring, is that it is extremely inefficient, requiring a substantial amount of the technician's time to perform the necessary operations, possible excess withdrawal, and there is a possibility of contact with the blood thereby contaminating the blood for further testing and possibly contaminating the technician with diseases carried in the blood. In the second system, the disadvantage is that the extraction needle may inadvertently draw up plasma, or accidently enter the separating gel barrier in an attempt to get the last of the serum thereby plugging the needle.
The following is a list of prior art references which discuss varying embodiments of liquid separation and inspection techniques.
U.S. Pat. No. 4,449,964 to Westberg et al. is directed to a decanting centrifuge for processing liquid materials. The tubes holding the liquid to be decanted are centrifuged about an axis as defined by the rotor. The amount of liquid to be decanted is controlled by the position of the rotor as it controls the amount of liquid to remain in the tube.
U.S. Pat. No. 3,401,876 to Lucas is directed to a similar type centrifuge as Westberg et al. with an additional axis of rotation. In this invention, the sampling tubes remain upright and the liquid material is decanted during centrifugation due to gravitational forces. This causes the lighter liquids to rise up and out of the tube.
U.S. Pat. No. 4,708,940 to Yoshida et al. is directed to an apparatus for analyzing body fluids such as blood. The apparatus includes a sampling section, i.e., a centrifuge, and an analyzing section. The liquid to be tested, Which has been placed in a series of tubes, is positioned in the centrifuge for separation. After separation, a withdrawing pipe is lowered to the tubes and plunged into the separated liquid components. A liquid level sensing electrode detects the depth of plunge and halts the lowering operation at a set level. The liquid is then withdrawn and pipe-pumped to the analyzer. Various measurements of the components of the liquid are then calculated by a data processing unit and the result of the analysis is displayed on a CRT display and recorded on a printer.
U.S. Pat. No. 4,358,425 to Finney et al. is directed to a tube for use in a centrifuge having a penetrable end by needle for drawing a sample of centrifuged liquid.
U.S. Pat. No. 4,847,205 to Burtis et al., U.S. Pat. No. 3,565,582 to Young and U.S. Pat. No. 4,698,311 to Hall et al. are directed to centrifuges in general and their medical applications.
U.S. Pat. No. 4,169,060 to Columbus is directed to a tube for collecting and separating a two-phase liquid, such as blood. The tube includes a partition, which can be used to separate serum from plasma, thus allowing serum to be easily removed by pouring. The partition can be an inorganic thixotropic polymeric gel, which is inert to blood serum.
U.S. Pat. No. 4,615,866 to Hyde et al. is directed to a fluid sampling and analyzing system, in which quantities of serum are withdrawn from a specimen container for analysis. The serum is withdrawn from an upright container by a tube attached to a pump.
U.S. Pat. No. 4,927,545 to Rocinski is directed to an apparatus for automatically sampling and analyzing blood serum. The apparatus includes a centrifuge, an optical sensing unit for receiving information from the centrifuged test tubes, an aspirator needle, which is designed to be placed in an upright test tube for withdrawing fluid, and a computer designed to analyze the output signals of the optical sensing unit.